Recently, it is on the rise to use a light emitting diode (LED) as a light source. More than several thousands lumina of luminous power are, generally, required to use the light emitting diode as a light source for specific applications such as illumination. The luminous power of the light emitting diode is substantially proportional to input power. Therefore, high luminous power is obtained by increasing the electric power inputted to the light emitting diode. However, the increase of the input power raises also the junction temperature of the light emitting diode. The increase of the junction temperature of the light emitting diode causes the loss of photometric efficiency which represents the conversion rate of input energy into visible light. As a result, power consumption increases considerably. Therefore, it is required to prevent the increase of the junction temperature of the light emitting diode due to the increase of input power. For the purpose, it is proposed a light emitting diode package in which the light emitting diode is attached on a heat sink, and the heat generated from the light emitting diode is dissipated through the heat sink.
The light emitting diode package (hereinafter, LED package) employing the heat sink is disclosed in U.S. Pat. No. 6,274,924 B1, entitled “Surface Mountable LED Package” from Carey et al.
FIG. 1 is a perspective view illustrating the LED package 100 disclosed in the U.S. Pat. No. 6,274,924 B1.
Referring to FIG. 1, a heat sink 103 is placed into an insert-molded lead frame 101. The lead frame 101 is a plastic material molded around a metal frame. The heat sink 103 may include a reflector cup 113. A light emitting diode (LED) die 105 is mounted directly or indirectly via a thermally conducting submount 109 to the heat sink 103. Bonding wires (not shown) extend to the metal lead terminals 111 on the lead frame 101 from the LED die 105 and the submount 109. The lead frame 101 is electrically and thermally isolated from the heat sink 103. In addition, an optical lens 107 may be added to the package.
As a result, the LED die 105 is maintained at a low junction temperature because the LED die 105 is thermally coupled on the heat sink 103. Therefore, it is possible to obtain high luminous power since relatively high input power can be supplied to the LED die 105.
However, using only one LED die limits the increase of the luminous power. To overcome such a limitation, it is necessary for a plurality of LED dies to be mounted in one LED package. However, mounting a plurality of LED dies to one heat sink 103 limits an electrical connecting scheme. That is, the electrical connecting scheme of the plurality of LED dies with the heat sink 103 and the lead terminals is limited. Further, in order to assure uniformity of emitted light, it is necessary for the plurality of LED dies, which have the same structure and emit the same wavelength of light, to be mounted on the LED package. However, in the case that the plurality of LED dies, which have the same structure and emit the same wavelength of light, are mounted on one heat sink 103, the input current for driving the LED dies considerably increases since all the LED dies are connected in parallel.
An additional submount may be used for preventing the increase of the input current and emitting uniform light. However, use of the submount complicates fabrication processes of the LED package and increases manufacturing cost thereof.
Meantime, it is required to provide a high power LED package capable of embodying polychromatic lights adapted to meet a variety of applications. An LED die, generally, emits a single wavelength of light. Therefore, LED dies emitting a variety of wavelengths of light should be mounted in one LED package in order to embody the polychromatic lights. Also, the LED dies emitting the various wavelengths of light should be driven respectively. For the purpose, it is needed to control the power supplied to each of the LED dies.